In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of improving spectral efficiency and further improving data rates, by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), it is performed exploiting maximum features of the system based on W-CDMA (Wideband Code Division Multiple Access). For the UMTS network, for the purpose of further increasing high-speed data rates, providing low delay and the like, Long Term Evolution (LTE) has been studied (3GPP Release 8).
In the 3G system, a fixed band of 5 MHz is substantially used, and it is possible to achieve transmission rates of approximately maximum 2 Mbps in downlink. Meanwhile, in the LTE scheme system, using variable bands ranging from 1.4 MHz to 20 MHz, it is possible to achieve transmission rates of maximum 300 Mbps on downlink and about 75 Mbps on uplink. Further, in the UMTS network, for the purpose of further increasing the wide-band and high speed, successor systems to LTE have been studied (for example, LTE Advanced (LTE-A)). For example, in LTE-A, the widest system band of 20 MHz in the LTE specification is scheduled to be extended to about 100 MHz.
Further, the LTE scheme system adopts multi-antenna radio transmission techniques such as the MIMO (Multiple Input Multiple Output) multiplexing method, and actualizes fast signal transmission by transmitting different transmission signals parallel from a plurality of transmitters using the same radio resources (frequency band, time slot) to spatially multiplex. In the LTE scheme system, it is possible to transmit different transmission signals parallel from four transmission antennas at the maximum to spatially multiplex. In LTE-A, the maximum number (four) of transmission antennas in the LTE specification is scheduled to be increased to eight.
In addition, in the LTE scheme system, when a transmission error occurs in an information bit, the receiver makes a retransmission request, and in response to the retransmission request, the transmitter performs retransmission control. In this case, the number of blocks (hereinafter, referred to as “retransmission blocks”) each of which is a retransmission unit in performing retransmission control is determined corresponding to the number of transmission antennas irrespective of the system bandwidth (for example, Non-patent Literatures 1 to 3). Described herein are the relationships in the LTE scheme between the system bandwidth, the number of transmission antennas and the number of retransmission blocks (the number of TBs), the retransmission block size (BS). FIG. 13 is a table showing the relationships in the LTE scheme system between the system bandwidth, the number of transmission antennas and the number of retransmission blocks, the retransmission block size. In addition, FIG. 13 shows 1.4 MHz, 5 MHz, 10 MHz and 20 MHz as the system bandwidth. Further, the “layer” as shown in FIG. 13 corresponds to the number of transmission antennas.
As shown in FIG. 13, in the LTE scheme system, irrespective of the system bandwidth, a single retransmission block is set in the case of a single transmission antenna. Similarly, the number of retransmission blocks is set at two in the case that the number of transmission antennas is two, and also the number of retransmission blocks is set at two in the case that the number of transmission antennas is four. In other words, when the number of transmission antennas is two or more, the number of retransmission blocks is equally set at two. In addition, the retransmission block size of the LTE specification is set at 150,000 bits at the maximum. FIG. 13 shows the case that the retransmission block size is set at 150,000 bits when the number of transmission antennas is four, and that the retransmission block size is set at 75,000 bits when the number of transmission antennas is two or less.
Herein, FIG. 14 shows a conceptual diagram of the retransmission block transmitted from the transmission antenna in the LTE scheme system. As shown in FIG. 14, in the case of a single transmission antenna, the retransmission block size is set at 75,000 bits, and a transmission signal A of 75,000 bits is transmitted from a transmission antenna 1. Further, in the case of two transmission antennas, the retransmission block size is set at 75,000 bits, and transmission signal A and transmission signal B each of 75,000 bits are transmitted from the transmission antenna 1 and transmission antenna 2, respectively. Furthermore, in the case of four transmission antennas, the retransmission block size is set at 150,000 bits, transmission signal A and transmission signal B each of 75,000 bits are transmitted from the transmission antenna 1 and transmission antenna 2, and transmission signal C and transmission signal D each of 75,000 bits are transmitted from transmission antenna 3 and transmission antenna 4, respectively.